1. Field of the Invention
The present invention relates to the manufacturing of semiconductor light-emitting devices using InGaAlN-based (InxGa1-xAlyN1-y, 0<=x<=1, 0<=y<=1) semiconductor material. More specifically, the present invention relates to a technique for minimizing the risk of damaging epitaxially fabricated InGaAlN-based light-emitting diodes during back side processing, testing, and packaging.
2. Related Art
Group III-V nitride compounds (e.g., GaN, InN, and AlN) and alloy compounds (e.g., AlGaN, InGaN, and AlGaInN) have been widely used in the manufacturing of light-emitting diodes (LEDs) and laser diodes that generate efficient luminescence. Techniques for epitaxially growing LEDs with group III-V nitride material include metalorganic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), and hydride vapor phase epitaxy (HVPE).
The manufacturing of LEDs typically involves the following stages: front side processing, back side processing, testing, and packaging. During front side processing, a wafer is prepared, and LEDs are fabricated by epitaxially growing InGaAlN-based (InxGa1-xAlyN1-y, 0<=x<=1, 0<=y<=1) multilayer structures on the wafer. During back side processing, the wafer is diced to separate individual LEDs. Subsequently, each LED is tested and packaged.
Wafer bonding is one of the techniques used in the fabrication of LEDs with vertical-electrode structures. Such a fabrication process begins with fabricating an InGaAlN-based multilayer structure on a silicon growth substrate. Next, the InGaAlN-based multilayer structure is coated with a layer of metal bonding material, and a conductive substrate coated with a metal bonding layer is prepared separately. The InGaAlN-based multilayer structure and the conductive substrate are then pressure-welded using the metal bonding layer. The silicon growth substrate is subsequently removed using a wet etching technique. This way, the InGaAlN-based multilayer structure is transferred from the silicon growth substrate onto the conductive substrate, and the multilayer structure is turned “upside down.” LEDs manufactured this way can benefit from a vertical-electrode configuration which results in high luminance efficiency.
However, the bond formed between the InGaAlN-based multilayer structure and the conductive substrate may not always be sufficiently strong to withstand the subsequent processing and testing. Specifically, the bond created by pressure-welding two unevenly surfaced bonding materials reduces the integrity of the contact surface and weakens the bond strength. As a result, LEDs fabricated using wafer bonding may crack when subjected to external forces in the subsequent testing process. For example, when a vacuum suction gripper lifts a device, the external force from the vacuum suction may cause the device to crack at the contact points between the device structure and the vacuum suction aperture.